Well as far as I know, East Kaioshin doesn't have a predecessor (never named, never mentioned) except Old Kaioshin. I interpreted Old Kaioshin being from 15 generations to literally mean 15 generations have gone since Old Kaioshin was sealed in a sword with no successor.

Buu managed to stay under the radar of the Kaioushin until Bibi-di started using him, so it wouldn't be all that unreasonable for the excessively lazy Beerus to not be aware of him either for the same reason.

Whis or the Oracle Fish must have told Beerus at some point. They certainly keep him updated in DBS about tons of stuff, so it seems unreasonable for Beerus to go through decades/centuries/millennia without hearing about Bibidi.

Buu canonically destroyed a lot of galaxies, and that is exactly the type of behavior that would've pissed off Beerus.

I had my numbers mixed up a bit. Those were values I had remembered seeing for Fat Buu himself, which would still put him over the likes of Ssj2 Goku (who would be 9 billion if he were at 4.5 billion in his Ssj form)

4.5bn x 2.5 = 11.25bn SSJ2 x 4 = 45bn SSJ3 (DBS)

Meanwhile SS3 Goku canonically is not much higher than Buu's supposed 14bn, so let's be generous and say 20bn...

Between SS3 Goku's first appearance and his appearance in DBS, Goku got over TWICE as strong in his base form? C'mon.